1. Field of the Invention
The present invention relates to a video signal processing device, and more particularly to a device for coding a luminance signal and color signals contained in a color video signal.
2. Related Background Art
Video signals such as television signals are now processed as digital signals in many cases. A digital video signal is represented by three primary color signals, typically R, G and B, or a luminance signal and two color difference signals. It is known that the visual sense of human eyes has a lower sensitivity to color change than to luminance change. Therefore, even if the sampling frequency of the color difference signals is made low to reduce the data amount, images can be transmitted without making them visually poor.
In transmitting (which term is to be taken through this specification and claims as including recording and reproducing) such video signals, image data is generally divided into blocks, a transmission error being corrected on a block unit basis, and the transmission error being prevented from propagating to another block. If each block is arranged to contain the luminance signal and color difference signal for the same number of pixels, a color image can be reproduced from only one block containing the same number of pixels of the luminance signal and color signal.
For example, if one data block is set to have an integer multiple Nx . . . ) or sub-multiple (l/nx . . . ) of a horizontal line or lines by setting the sampling point number ratio of each horizontal (H) direction line (each horizontal line) as Y : C1 : C2=2 : 1 : 1, and the vertical direction total sampling point number (horizontal line number) ratio as Y : C1 : C2=1 : 1 : 1, wherein Y represents the luminance signal (signal Y), and C1 and C2 represent two types of color difference signals (signal C), then it is possible for each data block to contain the same number of pixels of luminance data and color difference data, as shown in FIG. 1A. Furthermore, in the case where signals C1 and C2 are line sequentially transmitted by means of color difference line sequential processing, if the number of horizontal lines for use in sampling signal C1 or C2 is made the same as that of horizontal lines of signal Y, then it is possible for each data block to contain a combination of signal Y and signal C1, and signal Y and signal C2.
The above-described conventional blocking method is effective for horizontal line direction blocking. Vertical line direction blocking has been required recently because of compression coding and other signal processings. The above conventional method is not suitable for such vertical line direction blocking. Specifically, if the same horizontal sampling point number for Y and C (C1 and/or C2) cannot be obtained from any combination of C1 and C2 as is the case where the total sampling point ratio thereof is set as 3 : 1 for example, the vertical line number (horizontal direction total sampling point) becomes different between signal Y and signal C. Therefore, it is not possible for one data block to contain the same number of pixels of signals Y and C.